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Reaction of Me3Al with a series of aromatic ketones results in the precipitation of either dimethylaluminium enolates or alkoxides. In situ 1H-NMR spectroscopic studies of the reaction between Me3Al and acetophenone reveal a complex mixture of products whereas under the same conditions 2,4,6-trimethylacetophenone reacts cleanly to give the corresponding enolate. The enolate compounds [Me2AlOC(2,4,6-Me3–C6H2) CH2] (2) and [Me2AlOC(C6Me5) CH2] (4) were isolated and 2 as well as the representative alkoxide [Me2AlOCMe2Ph] (6) were characterised by X-ray crystallography. Both 2 and 6 form dimers with a central Al2O2 core. Ab initio molecular orbital calculations (HF/6-31G*) indicate that both 2 and 6 are the thermodynamic products of their reactions. For 2,4,6-trimethylacetophenone enolisation is preferred over alkylation by 4.70 kcal mol−1 whereas for acetophenone alkylation is preferred by 25.39 kcal mol−1 over enolisation. Disubstitution of the ortho positions on the aromatic ring by methyl groups results in the relative destabilisation of the alkoxide compared to the enolate due to steric crowding around the quaternary carbon atom.

In order to stabilise the alignment of liquid crystalline main chain polymers obtained by photopolymerisation of liquid crystalline thiol-ene molecules, a crosslinkable liquid crystalline thiol-ene...

The Hauser base reagents Pri2NMgCl 1 and Pri2NMgBr 2 react with a variety of enolisable ketones to yield magnesium enolates. Attempts at isolation of these enolates when THF was present in the solvent media was unsuccessful, with the exclusive precipitation of the solvated dihalide salts (MgX2 · Sx, where X=Cl or Br and S=THF, TMEDA or HMPA). Using diethyl ether as solvent media and one molar equivalent of HMPA, the halomagnesium enolate compounds [{ButC(CH2)OMgBr · HMPA}2] 3 and [Me2CHC(CMe2)OMgBr · HMPA] 5 were isolated and identified. Both 3 and 5 precipitate as mixtures with the dihalide salt [MgBr2 · (HMPA)2] 4. X-ray crystallographic studies reveal 3 to be dimeric utilizing enolate bridges, whereas 4 is a simple monomer. A molecular-orbital theoretical study (HF/6-31G*) was conducted to determine the relative bridging abilities of several model anions. The enolate anion H(CH2)CO− was determined to be a favoured bridge in preference to the halides F−, Cl− and Br−, which is consistent with the X-ray evidence. The amido anions Me2N−, (H3Si)2N− and (Me3Si)2N− are also calculated to be favoured over the chloride anion in three-coordinate dimer systems. This is contrary to the known structure of [{(Me3Si)2NMgCl · (Et2O)}2] 8 which bridges through the chloride atoms. The influence of solvent may be critical in determining which anion bridges. Solvent also plays a decisive role in the dismutation reaction of Hauser bases or halomagnesium enolates into their homoleptic components, similar to the Schlenk equilibrium for Grignard reagents.

The controlled reaction of molecular oxygen with hydrocarbon solutions of tBuLi results in the unexpected formation of the octameric species [(tBuOLi)8], 18. Single-crystal X-ray diffraction studies indicate that the connectivity within 18 corresponds with the fusion of two face-opened tetrameric cubanes. Cryoscopic studies establish the stability of the octamer in benzene solution, but heating results in aggregate rearrangement to the commonly found prismatic hexameric form, 16. Theoretical calculations confirm that the hexameric form is the thermodynamically favored aggregate.

The reactions of magnesium and calcium bis(hexamethyldisilazide) with propiophenone have been studied with a view to determine the utility of these bases in the stereoselective enolization of ketones and to uncover the nature of the metal enolate intermediates produced. Both base systems are highly Z-selective when the reactions are conducted in the presence of polar solvents. However, in situ monitoring of the magnesium system in arene solution revealed a preference for E-enolate formation, which was confirmed by silyl enol ether trapping studies. Solution NMR studies of the magnesium system in toluene-d8 show the presence of a monomer-dimer equilibrium for the intermediate amidomagnesium enolates. This assignment is supported by the characterization of a disolvated amidomagnesium enolate dimer by crystallographic analysis. Comparative studies of the calcium system show distinctly different behavior. This is exemplified by the characterization of a novel solvent-separated ion pair complex and a monomeric amidocalcium enolate in the solid state. Solution NMR studies of the calcium system in pyridine-d5 reveal the co-existence of the heteroleptic amidocalcium enolate, the bisamide, the bisenolate and the ion pair complex.

A reactive magnesium enolate intermediate has been identified containing the remarkable composition of four metals, eight enolates (six bridging and two terminally bound) and two unenolised ketones, and its implications in the aldol addition reaction are discussed.

Bis(hexamethyldisilazido)magnesium has successfully been used to mediate aldol additions of selected ketones and aldehydes in hydrocarbon media, and the structure of an intermediate amido(aldolate), [{(Me3Si)2NMg[µ-OC(Me)- ButCH2C(But)=O]}2] 17, produced by the self-coupled reaction of pinacolone has been characterised by X-ray crystallography.

The in situ reaction of Bu 2 Mg with 2 mol. equiv. of (Me 3 Si) 2 NH followed by addition of Ph 2 CO yields the heteroleptic amide/alkoxide complex [{(Me 3 Si) 2 NMg[µ-OC(H)Ph 2 ] ·(OCPh 2 )} 2 ] 1, whereas reaction of purified [{(Me 3 Si) 2 N} 2 Mg] 2 with Ph 2 CO results in formation of the solvate [{(Me 3 Si) 2 N} 2 Mg·(O CPh 2 ) 2 ] 3, the difference being due to incomplete amination of the bis(alkyl)magnesium compound resulting in β-hydride transfer to the ketone, which is the first example of this type of transformation using an alkyl(amido)magnesium reagent.